The present invention relates generally to axial flow fans having variable pitch blading and particularly to the lubrication of anti-friction type bearings used in mounting the blades to the fan rotors.
In the type of fan under consideration, the quantity of air being delivered by the fan is controlled by angularly shifting the blades about their central axes. It is advantageous to minimize the force required to shift the blades during operation in order that the variable pitch blade drive be of reasonable dimensions while retaining some reserve capacity. Accordingly, one should use anti-friction type bearings when mounting the blades to the fan rotor even though the infrequent and relatively small movement required of these blades is not a normal application for these type bearings. Such application has led to malfunctions of the bearings and associated lubrication systems and has resulted in rapid increases in blade shifting forces to values exceeding the drive motor rating. Moreover, difficulty has been encountered in the selection of lubricants and lubricant seals for anti-friction type bearings when subjected to the centrifugal forces and varying temperatures experienced during operation of the fans. Grease type lubricants have been found to breakdown under these operating conditions and have resulted in the loss of oil contained in the grease thereby leaving a residue inadequate for lubrication. Difficulty has also been encountered with providing effective long term lubricant seals for these bearings, thus leakage of lubricant in varying quantities can be expected over the service life of the equipment.